Conventionally, to carry (transport) a liquefied gas such as a liquefied natural gas (hereinafter this will be referred to as “LNG”), a liquefied gas carrier (transportation vessel) including liquefied gas tanks is used. For example, as the liquefied gas carrier which carries the LNG, there is a liquefied gas carrier of a MOSS type, including a plurality of spherical liquefied gas tanks (cargo tanks: hereinafter this will be simply referred to as “spherical tanks”). Hereinafter, this liquefied gas carrier of the MOSS type will be exemplarily described.
As shown in FIGS. 5 and 6, a liquefied gas carrier 100 includes a plurality of spherical tanks 130 arranged in a forward and rearward direction of a hull 110 (hereinafter this will be referred to as a “hull length direction”). In this example, the liquefied gas carrier 100 includes four spherical tanks 130 arranged in the hull length direction.
FIG. 7 is a cross-sectional view showing a hull support structure of the spherical tank 130 disposed at the center portion of the hull. A pair of side shells 112 are provided on both sides of the hull 110 in a hull width direction to extend in the hull length direction. A pair of longitudinal bulkheads 113 are provided to extend in parallel with the side shells 112, respectively. A foundation deck 111 having a deck structure for supporting the spherical tank 130 is provided around the spherical tank 130. The spherical tank 130 is provided with a skirt (skirt structure) 135 which is a cylindrical structure for supporting the spherical tank 130 on the foundation deck 111. This skirt 135 is provided to extend downward from the equatorial segment of the spherical tank 130.
Further, an inner bottom plate 115 extending in the hull length direction is provided below the spherical tank 130. The both end portions of the inner bottom plate 115 in the hull width direction are connected to the foundation deck 111 via a pair of bilge hopper plates 117, respectively.
In the above-described conventional hull structure of FIG. 5, the foundation deck 111 provided at the center portion of the hull in the hull length direction, is located at a height H100 in the vicinity of a neutral axis in longitudinal bending of the hull.
As an exemplary prior art of the above-described hull structure, there is a hull support structure which supports a skirt extending downward from the equatorial segment of a spherical tank, on the upper surface of a foundation deck provided at a predetermined height position of the hull (see e.g., Patent Literature 1). In this hull support structure, foundation deck support sections of the skirt are partially located outward in the hull width direction relative to locations at which the bilge hopper plates are connected to the foundation deck.